1. Field of the Invention
The present invention relates to a multi-layer rubber hose particularly suitable as a fuel hose for cars obtained by vulcanization-adhesion of a fluorinated rubber layer with a nitrile rubber layer and a method for producing the same.
2. Description of Related Art
The main abbreviations used herein are as follows:
FKM=fluorinated rubber PA1 NBR=nitrile rubber PA1 PVC=polyvinyl chloride PA1 PHR=number of parts per 100 parts of a stock rubber (polymer)
The recent trend in fuels is increasing the use of alcohol-added gasoline as a car fuel for the purposes of effective utilization of petroleum resources, reduction of fuel cost and reduction of environmental pollution. The above alcohol-added gasoline (hereinafter gasohol) is obtained by adding methyl tert-butyl ether (MTBE) or an alcohol to gasoline.
NBR has been used as a material for an inner rubber lager of a fuel hose in contact with gasoline. However, NBR has an inferior resistance to the gasohol because the solubility parameter (SP value) of the gasohol is near that of NBR.
It has been proposed to form the inner rubber layer of fuel hoses with FKM which is superior to NBR in gasoline resistance and alcohol resistance, and also in physical properties such as temperature resistance, chemical resistance, ageing resistance, and the like. However, the cost of FKM is very expensive, typically 10 to 20 times that of the general-purpose rubbers such as NBR and the like, so that it is not practical to form the whole inner rubber layer with FKM.
Because of the high cost of FKM, it has been proposed to form a thin FKM layer on the inner surface of a NBR base layer of a fuel hose. It is difficult, however, to obtain good adhesion between the FKM layer and NBR layer by the known methods.
In order to solve this problem, various techniques have been proposed to vulcanization adhere the FKM layer to the NBR layer using a FKM compound and a NBR compound.
For example, U.S. Pat. No. 4,606,952 discloses a rubber laminate produced by vulcanization-adhesion of the FKM layer to the NBR layer. In this rubber laminate, the FKM layer comprises a FKM compound in which the vulcanization system is a polyol system using a quaternary ammonium salt as a vulcanization accelerator, and the NBR layer comprises a NBR compound obtained by compounding NBR, a stock rubber, into which a particular functional group having an active hydrogen has been introduced and an oxide of a metal selected from Groups II to IV of the periodic table.
Japanese Patent Applications Kokai No. 61-242840 and U.S. Pat. No. 4,806,351 disclose a rubber laminate produced according to-the above U.S. Pat. No. 4,606,952 except that the amount of the vulcanization accelerator in the FKM compound is specified and a general-purpose NBR (having no introduced function group) is used as the stock rubber.
In the above conventional multi-layer rubber hoses, a large initial interlaminar adhesive force between the FKM layer and NBR layer can be obtained. However, the interlaminar adhesive force decreases after being immersed in a gasohol (methanol-added gasoline).